The present invention relates generally to a double-headed piston type compressor and more particularly to a compressor having a rotary shaft which is provided with a rotary valve having an introducing port for introducing therethrough refrigerant from a suction-pressure region of the compressor into a compression chamber and also having a shaft seal between a front housing and the rotary shaft for preventing the leakage of refrigerant along the peripheral surface of the rotary shaft.
FIG. 6 shows a double-headed piston type compressor C of prior art. The left and right sides of the compressor C of FIG. 6 correspond to the front and rear sides thereof, respectively. The compressor C has a housing assembly which includes a pair of cylinder blocks 80, a front housing 81 connected to the front end of the cylinder blocks 80 and a rear housing 82 connected to the rear end of the cylinder blocks 80. The paired cylinder blocks 80 define therein a cam chamber 83. The cam chamber 83 accommodates a swash plate 85 which is integrated with a rotary shaft 84. The swash plate 85 engages with a double-headed piston 86 in such a way that the piston 86 is movable reciprocally in conjunction with the rotation of the rotary shaft 84 through the swash plate 85. In the compressor C, a compression chamber 87 is defined in each cylinder bore 80a formed in the cylinder blocks 80 by the piston 86, and a rotary valve 88 is provided for introducing refrigerant into the compression chamber 87.
To be more specific, a part of the rotary shaft 84 is formed so as to function as the rotary valve 88 for each cylinder block 80. The rotary valve 88 includes a supply passage 90 that axially extends in the rotary shaft 84 and communicates with a suction chamber 89. The rotary valve 88 is provided with an introducing port 91 for communication between the compression chamber 87 and the supply passage 90 thereby to introduce therethrough refrigerant into the compression chamber 87.
In the above-described compressor C, a shaft seal 92 is provided between the front housing 81 and the rotary shaft 84 and accommodated in a shaft seal chamber 81a formed in the front housing 81 for preventing refrigerant from leaking along the peripheral surface of the rotary shaft 84 and flowing out of the compressor C. The shaft seal 92 degrades early and deteriorates in sealing performance unless appropriately lubricated. Therefore, the compressor C has a lubricating structure for ensuring lubrication of the shaft seal 92, which is, for example, disclosed in the Japanese Patent Application Publication No. 2003-247486.
The lubricating structure includes a lubricating passage 93, the shaft seal chamber 81a, a communication hole 94 and the supply passage 90. The lubricating passage 93 is formed in the front cylinder block 80 and the front housing 81. The communication hole 94 is formed in the rotary shaft 84. The lubricating passage 93 connects the cam chamber 83 and the shaft seal chamber 81a for communication therebetween. The communication hole 94 radially extends through the peripheral wall of the rotary shaft 84 for communication between the supply passage 90 and the shaft seal chamber 81a on the outer side of the rotary shaft 84.
Pressure of refrigerant in the compression chamber 87 of the cylinder bore 80a during a discharge stroke of its piston 86 is higher than that in the cam chamber 83. For this reason, refrigerant in the compression chamber 87 tends to leak into the cam chamber 83 through a slight gap between the outer peripheral surface of the piston 86 and the inner peripheral surface of the cylinder bore 80a. This leakage of refrigerant increases the pressure in the cam chamber 83 higher than that of the supply passage 90 thereby to produce a pressure differential between the supply passage 90 and the cam chamber 83. As a result, refrigerant in the cam chamber 83 flows through the lubricating passage 93, the shaft seal chamber 81a and the communication hole 94 to the supply passage 90. Thus, lubricating oil contained in the refrigerant that has flowed into the shaft seal chamber 81a lubricates the shaft seal 92.
In the lubricating structure disclosed in the Japanese Patent Application Publication No. 2003-247486, the communication hole 94 radially extends through the peripheral wall of the rotary shaft 84 so for communication of the supply passage 90 and the shaft seal chamber 81a. This has caused some weak portions of the rotary shaft 84.
The present invention is directed to a double-headed piston type compressor that improves the strength of the rotary shaft while ensuring lubrication of its shaft seal.